Most modern vehicles include a vehicle radio that requires an antenna system to receive amplitude modulation (AM) and frequency modulation (FM) broadcasts from various radio stations. Many vehicle antenna systems include a mast antenna that extends from a vehicle fender, vehicle roof, or some applicable location on the vehicle to receive these broadcasts. Improvements in vehicle antenna systems have included the development of backlite antenna systems, where antenna elements are formed on a rear window of the vehicle. The antenna elements in the backlite antenna systems are typically made of a conductive frit deposited on an inside surface of the window. Additionally, vehicle windshield antennas, such as the solar-ray antenna disclosed in U.S. Pat. No. 5,528,314, have also been developed. The solar-ray antenna includes a transparent conductive film laminated between the inner and outer glass sheets of the windshield. The windshield and backlite antenna systems provide a number of advantages over mast antenna systems, including no wind noise, reduced drag on the vehicle, elimination of corrosion of the antenna, no performance change with time, limited risk of vandalism, and reduced cost and installation.
Advancements in vehicle communications technology has led to the need for various high frequency antenna systems to provide reception for different communication systems, such as radio frequency accessories (RFA), including keyless entry systems, cellular telephone, global positioning system (GPS), personal communication system (PCS), etc. Because these antenna systems operate at higher frequencies than the AM and FM frequency bands, the size of the antenna is reduced from AM and FM antenna systems. These high frequency antennas must be positioned on a vehicle at a location where the antenna radiation does not interfere with the conductive vehicle body. It has been suggested to incorporate high frequency antennas in the vehicle windshield or backlite in combination with the existing AM/FM antennas to provide an "antenna farm." See Research Disclosure No. 346,127, published 1993. In this design, the high frequency antennas are mounted on an inside surface of the inside glass sheet of the windshield along a top edge of the windshield so that they do not obstruct the view of the vehicle operator.
The antenna farm concept as it currently exists suffers from a number of drawbacks. For example, the available space on existing vehicle windshields for providing antennas is limited, and the number of antennas that may ultimately be required may exceed this available space. Additionally, it may be detrimental from an antenna performance standpoint to allow radiation from the antenna to enter the passenger compartment of the vehicle. Other disadvantages also come into play for providing so many high frequency antennas on the existing vehicle windshields.
What is needed is a structure that enables mounting of a plurality of high frequency antennas on a vehicle windshield or backlite glass that does not suffer from certain disadvantages, such as those mentioned above. It is therefore an object of the present invention to provide such a structure.